The present invention relates to a machine for cutting staple fibers. More particularly, it relates to machines of this type which have a machine frame, a rotatable cutter holder, a rotatable pressing member with a rotary axis inclined to the rotary axis of the cutter holder, a coupling between the cutter holder and the pressing member, and a drive for the cutter holder and the pressing member.
Known machines for cutting staple fibers which are recommended for cutting standard fibers are not suitable for loadings which occur during cutting fiber cables of extremely rigid material such as for example poly-p-phenylenterephthalamide. The cutting forces are very high due to the high strength. Machine parts undergo elastic and plastic deformations. As a result of the deformations the cutting geometry is unfavorably changed. This leads to errors in cutting and unfavorable staple diagram. The power consumption is significantly higher than in the case of standard fibers. With the use of hard metal cutters recommended for cutting high strength fibers, increased cutter breaks take place.
Some modern staple fiber cutting machines of different manufacturers are provided with a rotation symmetrical cutter holder arranged on a driven shaft. A plurality of uniformly distributed cutters extend from an outer surface for receiving a winding. A rotation-symmetrical pressing member is located opposite to the cutter blades and is freely rotatable without its own drive. In operation the winding is pressed against the cutter blades, and the cable is cut. The pressing member rolls rotatably on the winding. The drive moment which is required for it is transferred by friction from the winding to the pressing member. A corresponding tangentially directed friction force which produces a bending moment in the cutters acts between the winding and the cutter blades. A typical fiber cutting machine of this type is disclosed in the German document DE-OS 2,939,154.
It has to be mentioned that a special embodiment of this staple fiber cutting machine described in the German document DE-OS 3,108,096. Here the cutter holder is arranged on a driven shaft which is supported in a housing mounted on the machine frame. A part of the housing is formed as an inclined bearing bushing for the pressing member. The cutter holder and the pressing member are coupled for example by magnets. The magnetic coupling can transfer however only weak torque and serve only for driving the pressing member in rotation at a starting point before inserting of the cables, so that no sliding friction is produced between the winding and the pressing member during the start. The significantly higher drive moment required after reaching the stationary conditions is transferred similarly to the first mentioned machine, substantially through the winding from the cutter holder to the pressing member. The bending moments occurring in the cutters are reduced under the action of the magnet only in insignificant values.
Another staple fiber cutting machine with some similar structural elements is disclosed in the U.S. Pat. No. 3,062,082. Here the cutter holder is supported rotatably on a shaft part which is mounted at its one side on a machine frame. The pressing member is supported on a seal which is mounted on the shaft part and has a cylindrical inclined outer surface. A flexible ring disc is provided between the cutter holder and the pressing member to form a coupling. Such a coupling changes generally at a uniform angular speed into a non-uniform angular speed which is superposed by periodical fluctuations. The amplitude of the fluctuations depends on the value of the angle between the axes of the driven and driving system. The coupling can transfer only small torques.
Another staple fiber cutting machine is disclosed in FIG. 2 of the German document DE-OS 2,811,491. Its rotatably supported cutter holder has an outer surface provided with axis-parallel slots. A pressing member is supported in the hollow cutter holder on an inclined axle. On its periphery it is provided with radial fingers extending in the slots. The fingers in connection with the slots prevent a relative turning between the pressing member and the cutter holder and during the start transmit the required torque from the cutter holder to the pressing member. During the operation the pressing member performs a wobbling movement, so that the fingers reciprocate axially in the slots and simultaneously are periodically tilted. This movement assumes that the fingers have a substantially play in the slots. The non-uniform relative movement between the fingers and the lateral limiting walls of the slots result in local high surface pressure and sliding friction. In the case of a high loading this leads to excessive wear and noise generation, especially since lubrication of the interengaging parts contacting the fiber winding during the operation is not permitted due to the contamination risks. This arrangement is therefore not suitable to transmit high torques during continuous operation.
The same is true with the machine described in the German document DE-PS 3,240,657. In this machine an inner toothing of the pressing member engages in axial grooves of the rotatable cutter holder.
Other staple fiber cutting machines are also known in which in kinematic reverse of the above described machines, a ring-shaped cutter set is arranged immovably on the machine frame. The associated pressing member is formed as a wobbling disc which rolls in the operation on the winding without turning relative to the cutter holder. The cable to be cut is laid by a rotatable, flyer-like guiding member.
A staple fiber cutting machine of this type which includes some known features is disclosed in the German document DE-OS 2,722,788. The pressing member has radial fingers extending into the slots of the stationary cutter holder. As for the cooperation between the pressing member and the cutter holder and the torque transfer, the statements made with respect to the arrangement of FIG. 2 of the German document DE-OS 2,811,491 is true with respect to this machine as well. Its FIG. 1 shows some structural elements. The inner toothing of the pressing member engages here in axial grooves of the stationary cutter holder.
In the manual "Maschinenelemente" of Roloff/Matek, 11. Auflage 1987, Verlag Friedrich Vieweg und Sohn, Braunschweig/Wiesbaden, pages 414/415, synchronizing hinges are described. The synchronizing hinge has substantially an outer hinge member provided with running grooves, an inner hinge member also provided with running grooves, six balls and a ball cage. The balls located in the running grooves and guided by the ball cage transmit a torque up to a great angle from one hinge member to the other hinge member. It also transfers high torque and are used predominantly for the single wheel drive of motor vehicles and also in general machine building in the cases in which the angle changes during the operation.